Australia
September 18, 2007
A
GRDC funded study found
widespread multiple herbicide resistant annual ryegrass (Lolium
rigidum) in Western Australia (WA) and concludes there are
severe management and sustainability issues for graingrowers.
In less than 25 years, ryegrass across the WA wheatbelt has
evolved from being susceptible to being resistant to many
herbicides.
Randomly selected from 14 million hectares of WA wheatbelt, 500
cropping paddocks were visited at crop maturity, with ryegrass
seed collected from 452 of these paddocks.
Mechelle Owen, a researcher at the GRDC supported WA Herbicide
Resistance Initiative at the School of Biology, University of
Western Australia said 68 per cent of the ryegrass populations
were resistant to the Group A herbicide diclofop-methyl
(Hoegrass) and 88 per cent to the Group B herbicide sulfometuron
(Oust).
This was an increase of 20 per cent in frequency of resistance,
compared with resistance levels surveyed in the same agronomic
zone five years earlier.
According to Ms Owen, 64 per cent of the ryegrass populations in
the current survey displayed multiple resistance to both
herbicide groups (A and B)
Intensively cropped areas displayed higher frequencies of
resistant and developing resistance populations due to greater
herbicide selection pressure.
A concern is that 24 per cent of ryegrass populations were
developing resistance to trifluralin and eight per cent to
clethodim (Select). Both of these herbicides are relied on to
control Group A and B resistant ryegrass.
On a more optimistic note, most ryegrass populations are still
susceptible to the wheatbelt’s most popular knockdown herbicide,
glyphosate, with less than one per cent showing resistance.
Paraquat, triazines (e.g. atrazine, simazine) and trifluralin
are also effective on most ryegrass populations.
The future challenge is to sustain the effectiveness of these
herbicides by using more diversified cropping and farming
systems, with less overall reliance on herbicides and more
integrated management strategies. |
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